The invention relates to switching power supplies, and more particularly to multi-output DC-DC switching power supplies.
There are about fourteen basic topologies (basic block diagrams) commonly used to implement a switching power supply. Each topology has characteristics which make it a suitable candidate for use in a particular application.
One of the most fundamental switching power supply topologies is the "buck" converter or "step-down" switching regulator. The buck converter includes a switch, usually in the form of a transistor, whose "on" time is controlled so that a series of rectangular voltage pulses of adjustable width can be appropriately filtered to provide a well-regulated average DC output.
Other switching power supply topologies are better suited for use as DC-DC converters. A DC-DC converter is a device which converts a DC voltage at one level to a DC voltage at another level. The converter typically includes a transformer, having primary and secondary windings wound around a common magnetic core. By opening and closing the primary circuit for appropriate intervals, control over the energy transfer between the primary and secondary windings is accomplished. The transformer provides an alternating voltage whose amplitude can be adjusted by changing the number of turns of the primary and secondary windings. Moreover, the transformer provides DC isolation between the input and the output of the converter.
One of the most common DC-DC converter topologies is the forward converter. When the primary winding of the forward converter is energized by closing the primary circuit, energy is immediately transferred to the secondary winding.
Recently, in the field of switching power supplies, greater attention has been directed toward compactness, energy efficiency, and higher performance. As integrated circuits pack more features in smaller volumes, it becomes increasingly important that the size of the system's power supply also decreases. Moreover, the complexity of many systems have increased with different parts of the system's circuitry requiring different power supply voltages. Thus, power supply designers are faced with the problem of providing smaller power supplies with multiple outputs and better performance.